The research in this proposal will examine the regulation of (Na+,K+)-ATPase in vivo by norepinephrine and by a specific endogenous inhibitor of the enzyme. (Na+,K+)-ATPase is the enzymatic basis of energy-dependent Na+ and K+ transport and has a central role in the regulation of intracellular cation concentrations and, hence, of membrane potential, cell excitability, and energy utilization. The experiments in this proposal are in four parts. 1) Experiments examining regulation of (Na+,K+)-ATPase, and interactions between norepinephrine and thyroid or adrenocortical hormones in regulation of (Na+,K+)-ATPase, and interactions between noradrenergic regulation of (Na+,K+)-ATPase and other mechanisms of Na+ Ca++ transport. 2) Experiments on specificity of transmitter regulation of (Na+,K+)-ATPase will examine specificity with respect to a) transmitter, receptor subtype, and tissue, b) molecular form of enzyme, using polyacrylamide gel electrophoresis to separate the two forms of enzyme, and c) localization of enzyme regulated by norepinephrine, using radioautography. The latter experiments will provide pilot data for development of studies using positron emission tomography. 3) Experiments on the mechanism of the noradrenergic effects will examine (Na+,K+)-ATPase-mediated transport in vitro. Initial experiments will compare effects in synaptosomes, dissociated brain cells, and brain slices. Further experiments will examine transmitter specificity, effects of prior exposure to norepinephrine, hormone status, or treatment with psychoactive drugs in vivo, effects of electrical stimulation in vitro, and roles of cation fluxes and of cyclic nucleotides. 4) Experiments in man will use stimulation of cation shifts by endogenous catecholamines to develop a means for examining noradrenergic regulation of (Na+,K+)-ATPase in intact man. These studies will provide the basis for studies of noradrenergic regulation of (Na+,K+)-ATPase in normal man and in conditions related to functions of the norepinephrine-(Na+,K+)-ATPase system, including affective disorders, eating disorders, and disorders of neural arousal.